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State threatened species The Arkansas darter Etheostoma cragini is endemic to the Arkansas River basin. It typically occurs as isolated colonies in spring seeps and runs that have abundant vegetation (Cross 1967). Cross and Collins (1975) concluded that the specialized habitat of ~. cragini renders it suscepti- ble to extirpation, especially in times of extreme drought. Because its habitat is diminishing and populations exist as isolated colonies, Platt et al. (1973) proposed that special attention be given to this species. Lee et al. (1980) show three localities where the Arkansas darter has been found in Colorado. Two of the localities are of historical sig- nificance; Sells Pond in Canon City, Colorado (Jordan 1891) and a spring- fed arroyo near Limon, Colorado (Ellis and Jaffa 1918). These areas have been sampled and the darter was not found despite intensive collecting. The third locality is a spring slough paralleling Fountain Creek south of Fountain, Colorado. Following this discovery, I informed Lee et al. of the location prior to publication. This represented the first documented population of ~. cragini found in Colorado since 1918. Madson (1982), in a popular article on the Arkansas River, stated that I had discovered eight locations of ~. cragini in Colorado. Since completion of this article more information on the darter has accumulated so that a brief overview is appropriate. The distribution of E. cragini in Colorado is disjunct with two major population centers, the Big Sandy Creek drainage and the Fountain Creek drainage. Big Sandy Creek and its major tributaries are intermittent plains streams with sand/silt bottoms. Most of the flow is subterranean except in areas where the land relief allows permanent surface flow over short distances. These permanent water areas are located in the upper third of the drainage, and the darter exists as isolated colonies here. Fountain Creek, on the other hand, is a foothills stream exhibiting a shifting sand/gravel bottom, extreme turbidity and a highly variable flow regime. The Arkansas darter exists, for the most part, in spring-fed seeps and streams adjacent to Fountain Creek. Approximately 193 km separates these two subdrainages. Matthews and McDaniel (1981) reported on the occurrence of the darter in atypical habitats. Collections in Colorado also suggest the Arkansas darter's ability to withstand sub-optimal conditions, at least on a short- term basis. One darter was captured in Fountain Creek. Matthews and McDaniel suggested that darters found in habitats such as this might be waifs flushed down from small tributaries and springs after rains. Under short-term drought conditions the ability to withstand harsh conditions would be critical to the survival of the species. On a long-term basis this ability might allow the use of larger streams as dispersal avenues. However, it seems likely that large connecting rivers that could serve as avenues of dispersal are instead effective barriers to species like the Arkansas darter that are adapted to life in small clear tributaries and springs. Where small tributaries enter large rivers with sufficient fre- quency, waif dispersal from one habitable tributary to another is possible. But when large rivers flow for long distances through lowland areas the potential for dispersal in this means is minimal (Pflieger 1971). Within 7